This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is an exploratory laboratory-based evaluation of cellular immune response to immunization with hepatitis B surface antigen in HIV-infected and HIV-uninfected adolescents. This is a substudy of ATN 024 and ATN 025. This substudy will compare cellular immune response in responders and nonresponders to immunization and also evaluate the relationship of these factors to the persistence of known correlates of serologic protection for the hepatitis B virus.